The invention concerns an electronic musical instrument, and more particularly a method and apparatus for controlling the manner of music synthesis by such an instrument to obtain a more pleasurable music performance.
Electronic musical instruments that synthesize music belong to one of two categories. The first category encompasses those musical instruments which produce a musical tone output from at least one continuous input that is acted upon by a substantially linear transfer network. These instruments are referred to as analog synthesizers because the music output is analogous to the continuous input when the transfer function of the transfer network is taken into account. The second category encompasses those musical instruments which produce a musical tone output from a sequence of discrete samples of varying amplitudes as an input that is acted upon by a scaling network and by a digital to analog convertor. These instruments are referred to as digital synthesizers because the music output is a reconstruction of an input of a sequence of digital numbers representing the discrete samples of varying amplitudes when the action of the scaling networks and the digital to analog convertors are taken into account. An example of the latter is shown in U. S. Pat. No. 4,602,545 by David Starkey, which is hereby incorporated by reference.
This distinction is important because both categories of synthesizers may be controlled digitally using a microprocessor.
Both categories typically are required to play one or more new notes when all of the note synthesizing assets are currently active. This occurs when the number of new notes to be played by the synthesizer and the number of previous notes or portion thereof still being played as part of an initially predetermined duration exceeds the total number of note sythesizing assets. In sophisticated electronic musical instruments, for example those including electronic effects such as automatic accompaniment and complex instrument voices such as guitar; how to provide synthesizing assets for a new tone when all sythesizing assets are currently active generating previously assigned tones or portions thereof is a significant and difficult design problem. Delaying the production of new tones until sythesizing assets are available may change the rhythm and be objectionable, while removing currently active sythesizing assets in order to reassign them to the production of the new tone or portion thereof may also be objectionable.
Analog synthesizers take advantage of the predetermined continuous way that the envelope of each tone is shaped as an indicator of which note to remove and reassign its channel to a new note. The envelope of the notes has a predetermined shape defined for many instruments, such as percusion instruments, as attack, sustain, and decay until the key defining the note is released. After release, the envelope is quickly dampened to terminate any further tone production. Various methods for removing a currently active tone generator and reassigning it to the production of a new note have used some of the predetermined attributes of the note envelope.
U.S. Pat. No. 4,481,851 by Swain et al. discloses an electronic musical instrument which assigns the notes corresponding to newly depressed keys to the note generators which have the greatest amounts of time in the release portion of their envelopes. This is described in column 5 in lines 20 et seq. An objectionable problem occurs if all of the note generators are active and not in a release status. As described in column 9 lines 24 et seq., in such a case the instruction to produce a new note is stored, i.e. delayed, until at least one note generator is in a release status.
U.S. Pat. No. 4,570,520 by Deutsch et al. discloses an electronic musical instrument which maintains a data record of how long each tone generator has been active with its current assignment. If a new key is depressed while all tone generators are currently active, then the tone generator that has been active on its current assignment the longest is reassigned to produce the tone corresponding to the newly depressed key. This method can be objectionable because it does not discriminate between musically important long notes such as bass tones, on the one hand, and less important tones which are not as prominent in the musical performance. This method is detailed at column 5 in lines 11 through 38.
U.S. Pat. No. 4,703,680 by Wachi et al. discloses an electronic musical instrument which truncates the tone which has the greatest amount of decay as described in column 6 lines 48 et seq. This instrument also has a provision for weighting the decay of the notes as a function of frequency, as well as, very simply prioritizing the lowest note in order to overcome one of the problems of removing musically important notes. This system suffers from the problem inherent in the design of analog system in that the note generator produces the entire sound for its respective note, and if it is the most important but most decayed upper note or the second most important and most decayed bass note, then it still will be completely removed leaving an objectionable void in the musical performance.
U. S. Pat No. 4,202,239 by Southard discloses an electronic musical instrument having two embodiments. The digital controlled analog synthesizer embodiment maintains a record of the oldest released note as described in column 10 lines 35 et seq. The analog controlled analog synthesizer embodiment compares the analog output of the top octave tone synthesizer with the output of a staircase voltage generator set at a level which is below the sustain level of the note envelope. This analog controlled embodiment removes and reassigns the note synthesizer which has the least voltage remaining out of its envelope keyer circuit (see column 20 lines 20 et seq.). This instrument suffers from the same problem as the other analog synthesizes previously mentioned in that it must remove an entire note in order to reassign the note synthesizer. Furthermore, in the Circumstances described at column 18 line 18 et seq., this known design will fail to sound a newly played note in favor of the notes currently active which may be very objectionable to those listening to the musical performance. Moreover, the analog measuring method for determining which tone generator to reassign simply takes too much time to be used in a digitally controlled system such as its own alternate embodiment.
Additional patents of interest are U. S. Pat. Nos. RE 31,931; 4,472,991; 4,387,617; 4,079,650; and 3,610,806.